So, I'm trying to lay out the exhaust of the LS-powered MGB. I'm going to be able to run a dual setup, woohoo! Based on how I'm running the pipes, though, the only way I'm going to get an X pipe out of this thing is if I have bends closer to 60 degrees than 45. I'm wondering if simply running a straight H pipe would be just as effective at that point. It certainly would be easier to do!
Thoughts?
I think you are going to be making enough power it wont matter too much.
I would think the greater the angle of interface, the less effective it would be. 45 > 60 > 90. But as Travis said, the power loss might be inconsequential.
I've read various things about both, and none of what I've read really makes sense. Other than from a pressure balance perspective.
It seems to my eyes and mind, that an X pipe has a problem with trying to squirt to gas flows through each other. That's never a good way to maximize flow. Various claims about timed sequencing all are hogwash as the timing does not match the claims.
An H pipe has its own directional flow, but gets screwed up by having a 90 degree angle to pulse through, if it goes that way. And the face of that 90 degree is there always screwing up flow.
Personally, I suspect both are fairly comparable in benefit. But, I've never done direct comparisons under controlled conditions to be certain of that.
H-pipes need to be installed at a specific place. For example, on my 350 at its operating range at need to be 15.9" or 31.8". Think of it as an energy wave cancelation chamber. There isn't a flow of exhaust going threw it, it just balances the pressure waves. In the wrong location, it will make a spike in the torque curve and drop power outside the spiked position on the curve . In the right position, it will sing a song. FWIW, if they didn't work, they would not be on a Nascar race vehicle. If you notice, they are near the collector. Just guessing, with their ci and rpm I bet they are 13-14" from the primary merge point. The X should go it a particular position also. But if you are off, the curve is so broad you will likely hit a range where you will gain what you want. And, you get the advantage of the exhaust and sound waves crossing which helps perf and sounds sweet. When you place the X at the correct position you feel it in the acceleration and the exhaust note is music.
I would contact the guys at Dr.Gas, theirs are 60-70-80*
I agree that I'm unlikely to be concerned with power levels. I'm actually more concerned with sound level and quality. But if I'm putting one of these things in, I'd like to do it right. And besides, it's a chance to learn.
wheels, thanks. That 15.9/31.8 measurement is from the collector? I'm constrained by packaging somewhat, but I could probably hit something in the latter range. Any suggestions on how to calculate where the correct spot would be for an LS1? 346 ci, mild cam, street rpm range?
It sounds as if the X has a much wider range so placement is less critical - is that right?
wheels, how did you determine what the location would be for you? is there some sort of formula? or is it trial by error? id like to hear the music!
I've had Mustangs with both an "H" pipe & an "X" pipe and strongly prefer the "X" pipe both for sound and power. As has been noted the location of each in the sxhaust system will effect the power peak and the sound. i prefer the sound of the "X" pipe. On my car, a Cobra 5.0 sans mufflers it sounded like it was turning 8K when it was only at 5K.
wheels777 wrote: FWIW, if they didn't work, they would not be on a Nascar race vehicle.
Isn't that an issue right there? Up until very recently they were trying to make the cars slower.
I have both a MAC off-road H (catless) and a BBK high flow catted X for my mustang (1997 4.6 4v) (had to get the X to meet visual inspection)
I havent really noticed a power difference, but I could be not noticing the power out of the X due to it being quieter. (those high flow cats shut it up a surprising amount).
the X has a sweeter sound, but I have been used to the rough sound of the H for years. I have a tendency to rev it higher with the X pipe (could be difference in sound or just volume, havent driven the car since fall)
I gotta spend some time looking up dyno tests and thinking.
After inspection I am trying to figure if I should put the H back on for the weight drop vs keeping the X for a small power gain. The car wasnt overly obnoxious to me without cats.
(side datapoint, flowmaster mufflers on the car terminating in stock location tailpipes)
Keith,
I don't know nuthin' about nuthin', but it seems to me that your question of optimal length is independent of chassis. In other words, find another car with similar engine and see what they do that works. If your engine is fairly stock, then see what worked for the factory.
My $0.02 probably isn't worth even that much, but maybe that helps.
David
It's independent of chassis - until my chassis won't let me put the pipe in a certain location 
The MG is a bit odd underneath, with a step change in the frame rail width. I'll be outside the frame rails until the middle of the car, then inside from that point. So I can't put in a crossover pipe until after I'm inside the rails, which is probably going to be a couple of feet from the collector at best.
If the X gives a better sound and a wider powerband, I'll find a way to make it fit.
itsarebuild wrote:PM me. It is alot easier to talk then type you through the process. For the stuff I do, I start with the cylinder head flow and cam timing, and walk my way thru the engine and exhaust. Some calculations are straight forward. Others, are applied to usage.wheels, how did you determine what the location would be for you? is there some sort of formula? or is it trial by error? id like to hear the music!
wheels777 wrote:itsarebuild wrote:PM me. It is alot easier to talk then type you through the process. For the stuff I do, I start with the cylinder head flow and cam timing, and walk my way thru the engine and exhaust. Some calculations are straight forward. Others, are applied to usage.wheels, how did you determine what the location would be for you? is there some sort of formula? or is it trial by error? id like to hear the music!
during the process, do you usually target a specific powerband and work to optimize within that range, or calculate something like a peak theoretical power for a particular setup (head/cam?) and work to broaden/shape the powerband within that range?
any favorite resources for research?
sorry for the hijack keith, but i figured you'd be interested in these answers as well.
Yup!
On a related note, I had my first look at the header packaging. I have very little room, so I think I'll just be shooting for low resistance instead of getting a good length. I simply don't have much room to play around. Half of the header is going to be in the wheel well already, and my biggest problem is going to be ensuring enough tire/exhaust clearance. Oh well. I suspect most of this exhaust system is just going to be "what fits".
